Upgrade the /gandi/init script to Python 3

[Seb35]

On a new server I created in Debian 12 (created in Debian 11 then upgraded to Debian 12), the script /gandi/init is crashing on startup (executed by gandi-bootstrap and gandi-postboot) because it is written in Python 2 but executed with Python 3 (see #11).

I open this task specifically to upgrade /gandi/init to Python 3; this file is not in this package but probably something in Gandi’s infrastructure, but it is interacting with this package and it is crashing gandi-bootstrap.

But together with #5 (when /gandi/init is written in Bash) there should be a better solution to execute this script, depending on its internal language: Bash, Python 2, Python 3.

[Seb35]

I did the following changes on the /gandi/init Python 2 script to upgrade it to Python 3:

• octal notation (3 changes): e.g. 0700 → 0o700
• function print (1 change): print … → print(…)
• function file() removed (25 changes): file('…') → with open('…') as f: (there may be opens in opens, so care should be taken about the variables names)